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Raspberry Pi “Moster” Heatsink Retaping

A pair of colorful laser-cut stacked acrylic Raspberry Pi cases with “Moster” (*) heatsinks arrived, with the intent of dressing up the HP 7475A plotters for their next Show-n-Tell:

Moster RPi Heatsink - assembled case
Moster RPi Heatsink – assembled case

Unfortunately, the thermal tape on one of the CPU heatsinks was sufficiently wrinkled to prevent good contact with the CPU:

RPi taped heatsinks - as received
RPi taped heatsinks – as received

The seller sent a replacement copper slug with tape on one side. Presumably, they glue it to the heatsink with thermal silicone:

Moster RPi Heatsink - silicone adhesive
Moster RPi Heatsink – silicone adhesive

Of which, I have none on hand.

So I did what I should have done originally, which was to drop a few bucks on a lifetime supply of thermally conductive heatsink tape, apply it to the bare side of the slug and stick the slug to the heatsink with their tape:

Moster RPi Heatsink - replacement adhesive tape
Moster RPi Heatsink – replacement adhesive tape

The blue stuff is the separation film, with the tape being white. It doesn’t match the black tape on the other side, but seems gooey enough to work.

Done!

Despite the heatsink hype, ball grid array chips dissipate most of their heat through their pads (and perhaps a central thermal pad) into the PCB, so sticking a heatsink atop the package is largely decorative, along the lines of hotrod ornamentation.

The epoxy packages used in previous Raspberry Pi iterations had better thermal conductivity to their top surface:

RPi 3 B - epoxy CPU
RPi 3 B – epoxy CPU

Than the more recent metal-top packages, which surely have inert-gas fill under the lid:

RPi 3 B - metal CPU
RPi 3 B – metal CPU

Pix cropped after being pilfered from the Official Raspberry Pi site.

Yes, the heatsink does conduct some heat into the air, even if not nearly as much as you might want.

(*) I’m pretty sure “Moster” was a typo in the original eBay listing which took on a life of its own to become something of an unofficial trademark. All of the search results ship from Duluth, Georgia (USA), regardless of the nominal seller; feel free to draw your own conclusions.

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  1. #1 by scruss2 on 2019-09-06 - 13:42

    I’ve never been able to get a 3B+/3A+ to go anywhere near thermal throttling, and I don’t have heatsinks on any of them. Your application may be different, though.

    The same can’t be said for the 4B, though. The tiny temperature-controlled fan I have on my 4 GB 4B (Pimoroni Fan SHIM) will cut in and out even when the system’s idle.

    • #2 by Ed on 2019-09-06 - 18:28

      I saw a note recently discussing how thermal throttling doesn’t appear in any of the usual Linux indicators, because it happens in the binary blob code running on the GPU and isn’t communicated to the OS.

      The mysterious vcgencmd seems useful, if awkward, to figure out what’s happening behind the scenes, although I can never remember the syntax.

  2. #3 by scruss2 on 2019-09-07 - 17:15

    vcgencmd get_throttled will show throttling status, though its definition of thermal throttling is a little more loose than most people would like. The Fan SHIM’s daemon just watches the CPU temperature reported in /proc and turns on at a very safe 60°C

  3. #4 by scruss2 on 2019-09-07 - 17:16

    I meant to add: this is a short guide to the get_throttled values from a Raspberry Pi engineer: https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=147781&start=50#p972790

    • #5 by Ed on 2019-09-08 - 08:34

      That looks familiar! [mutter]

      The “throttled” value is latched to means “has ever been throttled since boot”. That’s entirely reasonable, as it should never throttle in normal operation.

      A quick check of my always-on RPis says they’re all good: thanks for the pointer!

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